Grateful for any views anyone has on how I can best arrange for a trip to the US next year...

I am taking my wife, two children, and my parents to Florida. I have enough points for two UC returns and the original idea was for my wife and me to fly up front and pay for my parents and children to go PE (probably through a virgin Holidays package). But it seems a bit rough to expect my parents to look after the children both ways so the new idea is for my wife and I to go UC one way and then swap over with my parents having the UC seats for the return trip. We would still end up buying 4 PE seats - two adults, two children.

Given that we all have the same surname I'm wondering whether the easiest way is just to swap boarding cards after we have gone through the passport/boarding card check at the gate on the return trip - but am a bit worried that could cause problems. Also my parents don't travel much and I know they would feel uncomfortable in any thing they thought was underhand. On the other hand, I don't want to ask Virgin upfront in case they say that the only way to work it is to buy single fares or something stupid like that.

Any ideas on how best to make this work?